DC, AC or RF Sputtering using a magnetron and planar and cylindrical targets is known. On a planar or cylindrical target a plasma “racetrack” is formed and the target erodes to form an erosion region which follows the shape of the racetrack while the eroded material is deposited onto a substrate.
With a cylindrical target, the target material is a tube, which is rotated around its cylindrical axis. On the inside of the tube magnets are arranged that that are typically stationary with respect to a substrate to be coated.
Reactive magnetron sputtering is also known e.g. for the deposition of insulating (e.g. oxide or nitride of a metal) and semiconducting coatings. In reactive sputtering, the inert working gas is usually argon and the added reactive gas is often oxygen and/or nitrogen. The coating of dielectric materials can be accomplished by RF sputtering of the dielectric material itself used as the target but the deposition rates are very low. DC or AC reactive magnetron sputtering of insulating films can have higher deposition rates and lower costs, but there is a need to improve the quality of the deposited insulating metal oxides and nitrides, e.g. their variation in thickness and/or the chemical variability of the coating. Process control for reactively depositing insulating films at high rate traditionally has been difficult. Usually the substrate is moved continuously underneath the magnetron, in a direction perpendicular to the longitudinal axis of the cylindrical target. The instantaneous deposition rate over the deposition region is not always constant and the resulting film does not have a uniform stoichiometry.
U.S. Pat. No. 4,466,877 McKelvey describes a pair of rotatable cylindrical magnetrons mounted horizontally and spaced in a parallel relationship to each other such that the sputtered flux is directed inwardly and downwardly from each is focused on the same region of the substrate. U.S. Pat. No. 6,365,010 describes a magnetron system for eroding and depositing target material on a substrate, having a first and a second rotatable cylindrical tubular target, wherein the second rotatable cylindrical tubular target is positioned relative to the first target such that axes of the first and second targets are parallel to each other and the outside surfaces of the first and second cylindrical tubular targets are in close proximity.
The magnet assembly inside each target is configured to provide a magnetic field racetrack over the outer surface of each tubular target, the magnetic field racetrack confining a plasma gas to erode the target material of each target to create a combined area of target material flux for each tubular target, wherein a greater fraction of the target flux from each target is utilized to deposit target material on the substrate than from a single zone on each target. The magnet assemblies are oriented relative to each other such that, at the substrate, an included angle is formed between a pair of planes passing through the axis of each target, and the target flux of each of the targets combines to create an area of substantially uniform flux at the substrate.
Each of the methods previously described suffers from one or more of the problems commonly associated with reactive sputtering. What is needed is an improved sputtering apparatus and control process for high rate deposition of insulating and semiconducting films that provides uniform coatings. Film stoichiometry must be kept uniform throughout the thickness of the film. Additionally, the process must provide a uniform coating thickness.